A conventional testing apparatus using ultraviolet fluorescent lamps as shown in FIG. 1 has eight equal intensity ultraviolet fluorescent lamps 1 provided in a test chamber 2 and arranged in two symmetric downwardly divergent rows when viewed in cross-section. Specimens 3 to be tested are attached to two opposite specimen supporting walls of the housing of the test apparatus so as to face inwardly toward the fluorescent lamps and receive the light radiated therefrom. In the machine shown, there are two specimens, an upper and a lower one. However, there may be only a single specimen or more than two. The rear surfaces of the specimen 3 are exposed to the atmospheric air outside the machine. Outside air is drawn through a blower 5 and heated by a heater 6 and the thus heated air is blown into the interior of the chamber 2 through a hot air discharge port 4 to regulate the temperature in the chamber 2. Water in moisture supply tanks 7 is made hot by heaters 8 therein and evaporated to thereby supply moisture into the chamber 2.
An example of the use of this testing machine will now be described. In the above-described testing machine, the ultraviolet rays are applied to the specimens 3 at a temperature of 60.degree. C. for 16 hours, and the fluorescent lamps 1 are then turned off and the interior of the chamber 2 is kept at 50.degree. C. for 8 hours. These two steps, which constitute one cycle of a deterioration testing operation, are repeated continuously. While the fluorescent lamps are off, the humidity in the chamber 2 is high, and the rear surfaces of the specimens are exposed to the outside air at a low temperature. Accordingly, the surfaces of the specimens are wetted due to condensation. Thus, the wetting of the specimens, the applying of ultraviolet rays thereto, and the drying thereof are repeated, which speeds the deterioration of the specimens.
However, this testing machine has a large drawback in that the reproducibility of test results is low. When the same deterioration test of 3000 hours is carried out with a plurality of these testing machines, they require anywhere from 2000 to 4000 hours to obtain the same test results. Thus, the reproducibility of results using this type of testing machine is extremely low due to such a large error.